I would also be interested in this or animated thumbnails, like on:
www.imeem.com
I realise that xnview is mainly a photo viewer / editor, so the pressure to improve those parts are higher. But if there are other programs that do this that anyone knows about that support multiple video formats like xnview I would be very interested.
After reading about Intel demoing an app that showed the video thumbnails in a gallery actually playing on their new I7's, just looking at static one frame shots seems a bit behind the times..... Obviously it would need to be optional for people with lower end proccesors and not enough storage.
But even just 4 frames per thumbnail, start, 1/3, 1/2 and 2/3 of the way throught the video that started animating on mouse over would be a big help.....